Apparatus for starting an electric spark



Nov. 5, 1940. T. SHlMlZU ETAL 2,220,551

APPARATUS FOR STARTING AN ELECTRIC SPARK Filed Nov. 21, 1938 PatentedNov. 5, 1940 7 UNITED STATES PATENT OFFICE Takeo Shimizu and MorlsoHirata, Tokyo, Japan,

assignors to Zaidan Hoiin R-ikagaku Kenky i T k Japan ApplicationNovember 21, 1938, Serial No. 241,690

3 Claims. (c1. 176-1) 7 This invention relates to apparatus for startingan electric spark and comprises a triode, a positive spark-electrodeconnected to a plate of the triode, an electronic ray passage extendingfrom theplate to the positive spark-electrode, a thin metallic windowclosing thepassage, an opening provided in the positive spark-electrodeoutside the metallic window and in continuation to the passage, and anegative spark-electrode 10 arranged opposite the opening of thepositive spark-electrode. The object of the invention is to provideapparatus for'starting an electric spark which is very sensitive andsteady 'in the operation of starting the spark. In the accompanyingdrawing,

Fig. 1 is a diagrammatical view of one example of the apparatusaccording to the invention. Fig. 2 is a modification of the electriccircuit for controlling the grid voltage of the triode employed in thisinvention.

Fig. 3 is a modification ofthe triodeby which the positivespark-electrode and the plate side thereof are contracted together.

Fig. 4 is a sectional view of a preferable de-.

tailed construction showing the attachment of the triode and thepositive spark-electrode.

Fig. 515 an end view of the plate shown in Fig. 4.

In Fig. 1, I is a positive spark-electrode, 2 a

negative spark-electrode arranged opposite an opening I provided on theelectrode I. 3 is a triode having a filament 4, a grid 5 and a plate 6.The positive spark-electrode I. is made in one piece with the plate 6and sealed in the wall of the triode 3. The plate has a central passage8 for electronic rays extending from the plate 6 to the opening I of theelectrode I and the passage is closed by a thin metallic window 3' tokeep the vacuum in the triode. This window 8' may be for instance madeof nickel or aluminium so that the electronic rays or X-rays generatedthereby are penetrable therethrough. 9 iso circuit for the filament 4having a source of electricity or cell II. III is a circuit wire for thegrid '5 connected to a source of electricity or battery I2 through aswitch I5. An accelerating source of electricity or battery I3 ofslightly higher voltage than the battery I2 is associated with thecircuit I0 and a high resistance I4 is interposed. between the batteriesl2 and I3, and the switch I5 is arranged for short-circuiting the partcomposed of I3 and I4. The parts I0, I2, I3, I4 and I5 constitute meansof controlling the grid voltage of the triode.

- "In operation,-the electrode 2 'and th cell I I from the filament 4 tothe plate 6.

enough to generate electric sparks between the electrodes I and 2. Whenthe electrode I is highly charged, a great difierence of voltages 10occurs between the plate 6 and the filament 4. However, in this statethe voltage of the grid 5 is still negative so that no electrons canflow Then the key I5 is opened to afiect the grid 5 by the posil3 tivevoltage of the accelerating battery l3 and thereby electrons flowinstantly from the filament 4 to the plate 6. The speed of the flow ofelectrons thus generated is accelerated by the plate 6 under highcharge, the fiow fomiing high 0 speed electronic rays, which passthrough the passage 8, penetrate the thin metallic window 8', go out ofthe opening I of the electrode I and ionize air lying betweenthe twoelectrodes I and 2. When the thickness of the metallic window is over acertain extent, the cathode rays may not penetrate therethrough. In thiscase X-rays generated by the electronic rays in the neighbourhood ofthemetallic window 3', pass through the metallic window and ionize air out-30 side the opening I. It is well known that when air is powerfullyionized, the voltage difference necessary to generate electric sparks isgreatly decreased. Therefore by the ionization of air as abovedescribed, an electric spark is gener- 33 ated between the electrodes Iand 2. The time of duration of the spark varies according to the kind ofthe source of the voltage charging the plate 6 and the electrode I. Whena condenser is employed as the source, the spark instantly ,40diminishes. The metallic window 8' is preferably spaced from the outersurface of the electrode I so that damaging effects of the spark uponthe metallic window 8' can be avoided.

Fig. 2 shows another circuit for controlling 45 the grid voltage of thetriode. In this example, when the key I5 is opened, the grid voltage iskeptnegative and when it is closed, the

spark is started. The same numerals show corresponding parts shown inFig. 1.

. The actual closing and opening of the key I5 may be replaced bybreaking or connecting the circuit wire by means of a moving body ofhigh velocity, or the grid voltage may be controlled I indirectly by anyelectrical or optical stimulations. Therefore the apparatus can. beconveniently employed in the measurement of the velocity' of gunprojectiles or very short intervals of time, or in high speedphotograph-taking etc. The apparatus is excellent in that the timerequired from the closing or opening of the key to the start of spark isextraordinarily short and that the starting of the spark is very steady,so that great advantages are obtained in the practical applications ofthe apparatus such as above stated. I

Fig. 3 shows a modification of the triode and the positivespark-electrode. In this example, the electrode I and the plate 6 aremade to take the form of a metallic wall of the triode, and the outercentral part 01 the wall is somewhat outwardly curved to give aconvenient form for the generation of sparks. Same numerals showcorresponding parts to those in Fig. 1.

- The preferable embodiment oi attachment of the spark-electrode I tothe triode 3 is shown in Figs. 4 and 5, although this is' not anessential part of the invention. In this example, the plate 6 has acentral tubular extension '0, which is sealed in a copper tube I8, whichis sealed with respect to the glass walls 3 of the triode. The end ofthe passage 8 is closed by a thin metallic window 8' which is welded tothe end of the tubular extension 6'. The electrode I having an opening Iis cupped upon the copper tube It and is clamped by means of a stud boltII.

In the examples shown, the electronic ray passages extend continuouslyfrom the plate to the positive spark-electrode. essential and a part orthe passage may be replaced by a mere vacuum space'within the triode,and the plate and the spark-electrode connected to independent sourcesof potential.

What we claim is: 1. In apparatus for starting an electric discharge, anevacuated tube having a filament and However this is not a grid and aplate therein, said plate having a passage therein which terminates inan elec trode outside the tube, another electrode arranged outside thetube in a spaced relation with respect to said electrode, and arelatively thin metal window closing said passage and spaced from theouter end of the first mentioned electrode.

at a relatively high voltage without creating a discharge therebetween,another electrical source for biasing said grid positively wherebyelectrons may pass to the plate and penetrate the metal window forionizing air between the electrodes to start a discharge therebetween.

3. Apparatus for starting an electric spark comprising, a discharge tubehaving a plate therein, a positive electrode of a convex form connectedto the plate side of the tube and having an electronic ray passageextending irom the plate thereof to and through the positive electrodeand opening at the top of the convex surface thereof, a relatively thinmetallic window permitting the passage of the electron rays butmechanically closing the passage at a position slightly backward fromthe extreme end of the passage so as to providean opening outside themetallic window, and a negative electrode arranged opposite the opening.

TAKEO SHIMIZU. MORISO HIRATA.

